The present disclosure relates generally to optical detectors, and more particularly to characterization of single-photon detectors using a continuous wave laser source.
An optical detector that has a sufficiently high detection sensitivity that it can detect a single photon is referred to as a single-photon detector (SPD). Single-photon detectors operating over various ranges of wavelengths have been used for various applications, including ultrahigh resolution optical time domain reflectometry, photon-correlation spectroscopy, and device characterization. At present, there is particularly strong interest in the application of SPDs for optical telecommunications. One method for high-security transmission over an optical telecommunications network is quantum cryptography, which utilizes quantum key distribution via single photons. Fiberoptic transport networks typically operate over a wavelength range of ˜1.3-1.6 μm. Over this wavelength range, single-photon detectors are typically based on avalanche photodiodes (APDs) fabricated from InP/InGaAs/InGaAsP heterostructures.
A critical performance parameter characterizing an SPD is its detector efficiency. For optical telecommunications, SPDs typically have a low detector efficiency (˜10-30%); furthermore, the detector efficiency drifts with time. Current methods for measuring the detector efficiency of SPDs use complicated timing control schemes and ultralow input power levels. Current measurement equipment is typically bulky and expensive, including electronic time delays, pulsed lasers, high dynamic range attenuators, and high sensitivity power meters. What is needed is a simple, low-cost, compact system for measuring the detector efficiency, and other characteristics, of a single-photon detector.